Frost Dates for 99610 — Kasilof, Alaska

Half of springs at Soldotna 5SSW, AK see their last 32°F night by June 11; only one in ten is past it by May 26, and one in ten still has one after July 7. Planting tender crops after June 20 leaves a 30% risk of a frost on them, after June 26 20%, and after July 7 10%. The 26 days between the even-odds date and the one-in-ten date is the widest of the 37 Alaska stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.

In fall the first 32°F night comes by September 1 in half of years, as early as August 11 one year in ten, and holds off past September 18 one year in ten. A hard freeze of 28°F follows 15 days later, around September 16; in spring the one-in-ten date for 28°F is June 6, 31 days before the 32°F one. The freeze-free season lasts 75 days in a typical year, the shortest of the 37 Alaska stations; it reaches 100 days one year in ten and falls short of 48 one year in ten. On average 227 nights a year drop to 32°F or below. Severe cold of 16°F or below comes every winter, usually between October 19 and April 9.

July is the warmest month at Soldotna 5SSW, AK, averaging 66°F by day and 45°F at night; January is the coldest at 21°F and 5°F. A freezing night is all but certain in every month from September to May (a 90% chance or more). No month is safe from a 32°F night: even the warmest has at least a 10% chance. In spring, June still brings one in 69% of years and July still brings one in 16% of years.

Warmth for growing adds up to 373 growing degree days a year (base 50°F), fewer than at 89% of the 37 Alaska stations. 21% of them (80) have built up by the end of June, and July adds the most, 166. Precipitation totals 21.6 inches a year, most in September (4.0") and least in March (0.7"); May to September bring 52% of it.

The nearest other station, Sterling 6SW, AK, 17 miles northeast of Kasilof, has a last frost 22 days earlier (May 20), a first frost 20 days later (September 21), a season 48 days longer.

The first measurable snow (0.1 inch or more) in Kasilof usually arrives around October 22, and the last of the season around April 8. Those are the middle dates across the winters of 1991–2020 at Kenai 9N, AK, 24.3 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 64 days after the last snow.

ZIP 99610 is 9 miles from Soldotna 5SSW, AK, which stands at 180 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 99610 in zone 4b, the band where the coldest night of the year averaged -25 to -20°F (-31.7 to -28.9°C) over 1991–2020; a zone describes winter lows, not frost dates.